Consolidated Statements Of Changes In Shareholders Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive income (loss)
Balance at Dec. 31, 2012	$ 1,804,705	$ 176,406	$ 37,108	$ 1,036,295	$ (7,838)	$ 555,023	$ 7,711
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,052					32,052
Other comprehensive (loss) income, net of tax	(8,778)						(8,778)
Cash dividends declared on common stock	(3,328)					(3,328)
Dividends on preferred stock	(2,581)					(2,581)
Accretion on preferred stock	0	35				(35)
Stock-based compensation	2,413			2,413	0
Common stock issued for:
Exercise of stock options and warrants	115		9	320	(214)
Restricted stock awards	66		111	90	(135)
Employee stock purchase plan	641		13	628
Director compensation plan	383		31	352
Balance at Mar. 31, 2013	1,825,688	176,441	37,272	1,040,098	(8,187)	581,131	(1,067)
Balance at Dec. 31, 2013	1,900,589	126,477	46,181	1,117,032	(3,000)	676,935	(63,036)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,500					34,500	0
Other comprehensive (loss) income, net of tax	6,283						6,283
Cash dividends declared on common stock	(4,620)					(4,620)
Dividends on preferred stock	(1,581)					(1,581)
Stock-based compensation	1,681			1,681
Common stock issued for:
Exercise of stock options and warrants	2,270		77	2,464	(271)
Restricted stock awards	43		41	111	(109)
Employee stock purchase plan	600		13	587
Director compensation plan	378		20	358
Balance at Mar. 31, 2014	$ 1,940,143	$ 126,477	$ 46,332	$ 1,122,233	$ (3,380)	$ 705,234	$ (56,753)